An open flask is half filled with water at 25°C.

Phase equilibrium can be reached after

(1) more water is added to the flask

(2) the flask is stoppered

(3) the temperature is decreased to 15°C

(4) the temperature is increased to 35°C

An open flask is half filled with water at 25 degrees Celsius. Phase equilibrium can be reached after the flask is stoppered. Equilibrium is defined as a state of balance or a stable situation where opposing forces cancel each other out and where no changes are occurring. Thermodynamics is usually subdivided into a theory dealing with equilibrium and into one concerned with irreversible process.